Heretofore when it has been desired to connect a gauge to a high pressure head or line, such as a manifold for handling oilwell drilling mud, it has been the practice to use a large bore high pressure tee, a high pressure valve and a split flange to mount the gauge in such a manner that it could be isolated from the high pressure fluid in the manifold. Various other manifold-type devices have been provided in the past, such as the stack-type gauge isolator valves which are used in hydraulic circuits for selectively gauging various circuits. These devices, however, merely read the take off and are of a structure which would be unsuitable for use with high pressure fluids, such as oilwell drilling mud, which would cause the devices to plug up and become inoperable and further, such devices have no provision for injecting grease or other anti-solidifying matter into the bore to prevent a plug up of the pressure gauge passage.